Process for producing non-silicon bearing electrical steel

ABSTRACT

Non-silicon bearing electrical steel is produced utilizing steel from a basic oxygen furnace or open hearth with particular ranges of carbon and oxygen and degassing to reduce the levels of these constituents. The degassed material is formed into slabs, hot rolled, pickled, cold rolled and can be finished, annealed and used. Preferably the cold rolled product is annealed and subjected to cold working before use. By utilizing a particular degree of cold working subsequent to cold rolling and annealing significantly enhanced electrical properties are obtained compared to where there is no cold working or a lesser amount of cold working. Manganese and phosphorus may be added to improve both mechanical and electrical properties.

1 United States Patent [191 Decaro et a1.

1 1 PROCESS FOR PRODUCING NON-SILICON BEARING ELECTRICAL STEEL [75] lnventors: David P. Decaro; Gerald A.

Gronceski, both of Michigan City, Ind.

[73] Assignee: National Steel Corporation,

Pittsburgh, Pa.

22 Filed: July 31,1972

211 .Appl. No.: 276,325

[52] US. Cl 148/120, 148/121, 148/122, 143/3155 [51] Int. Cl. H011 U110 [58] Field of Search 148/120, 121,122,111, 148/31.55; 75/49 [56] References Cited UNITED STATES PATENTS 3,188,250 6/1965 Holbein et a1. 148/121 3,347,718 10/1967 Carpenter et a1 148/31.S5 3,387,967 6/1968 Perry et a1. 75/49 3,522,114 7/1970 Knuppel et al. 148/111 3,607,229 9/1971 Knuppel et a1. 148/120 1 June 25, 1974 3,615,903 10/1971 Perry 148/122 7 3,620,856 11/1971 Hiraoka 148/122 FOREIGN PATENTS OR APPLICATIONS 707,731 4/1965 Canada 148/121 Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Shanley & ONeil [57] ABSTRACT Non-silicon bearing electrical steel is produced utilizing steel from a basic oxygen furnace or open hearth with particular ranges of carbon and oxygen and degassing to reduce the levels of these constituents. The degassed material is formed into slabs, hot rolled, pickled, cold rolled and can be finished, annealed and used. Preferably the cold rolled product is annealed and subjected to cold working before use. By utilizing a particular degree of cold working subsequent to cold rolling and annealing significantly enhanced electrical properties are obtained compared to where there is no cold working or a lesser amount of cold working. Manganese and phosphorus may be added to improve both mechanical and electrical properties.

4 Claims, No Drawings PROCESS FOR PRODUCING NON-SILICON BEARING ELECTRICAL STEEL BACKGROUND OF THE INVENTION This invention relates to improvements in the manufacture of steel produced in sheet form for use in magnetic cores of electrical equipment.

Silicon-steel electrical sheet has been traditionally used for such cores. This is a relatively expensive product.

Relatively recently, non-silicon bearing electrical steels have made an appearance and are lower priced than silicon-steel electrical sheet. Canadian Pat. No. 707,731 discloses producing such steels by decarburizing plain carbon steel strip by open coil annealing and then critically straining the decarburized steel to obtain from about 1 percent to about 13 percent elongation. The open coil annealing operation is expensive.

Both the silicon-steel electrical sheet and the nonsilicon bearing electrical steel produced according to the method of the Canadian patent are box annealed to develop magnetic properties. This step denoted a magnetic anneal is customarily carried out at l,450 F.

It is an object of this invention to provide a method of producing non-silicon bearing electrical steel which is lower priced than silicon-steel electrical sheet and which eliminates the costly open coil annealing step required in the method of the Canadian patent.

It is a further object to provide an electrical steel which can be subjected to a magnetic anneal utilizing lower than the customary temperature of l,450 F. thereby speeding production, providing fuel savings and minimizing the possibility of sheets sticking to one another during such annealing.

These objects and others will be evident from the following detailed description.

DETAILED DESCRIPTION It has been discovered that the costly open coil an nealing step can be eliminated and advantages can be realized in the magnetic annealing step by producing steel with particular ranges of carbon and oxygen and degassing to reduce the levels of these constituents.

The steel is produced, for example in a basic oxygen furnace or open hearth, containing from 0.03 to about 0.7 percent carbon, preferably from about 0.045 to 0.06 percent carbon, and from about 300 p.p.m. to about 800 p.p.m. oxygen, preferably from about 450 p.p.m. to about 700 p.p.m. oxygen.

The steel so produced is subjected to vacuum degassing to reduce the percentage of carbon below 0.03 percent to a level exceeding 0.002 percent. Such degassing reduces the percentage of oxygen which is present and after degassing the oxygen content typically ranges from about 150 p.p.m.-to about 600 p.p.m. Preferably the steel is degassed so as to contain from about 0.008

or by casting into ingots and slabbing for example in a blooming mill.

The slabs are hot rolled with the temperature of the material leaving the finishing train preferably ranging from about l,450 to about 1,550 F. and very preferably ranging from about l,475 to about l,525 F. These are relatively low finishing temperatures in hot rolling.

The hot rolled material is coiled at a temperature ranging from about l,250 to about 1.400 F. and preferably is coiled at a temperature ranging from about l,300 to about l,350 F. which is a relatively hot temperature as compared to the conventional coiling temperature utilized after hot rolling of less than l,300 F.

It has been discovered that by utilizing the preferred hot rolling and coiling temperatures stated herein, that is by utilizing a low finishing temperature in hot rolling and a relatively high coiling temperature, that electrical properties in the finished product are improved. While this preferred variant of utilizing low hot rolling finishing temperatures and coiling hot is not required to obtain a good electrical steel utilizing the present process, it does provide a significant improvement in electrical properties in the finished product.

The coiled steel is pickled to remove scale formed during hot rolling. This pickling can be carried out for example by any conventional process and is preferably carried out utilizing hydrochloric acid.

After pickling, the material can be cold rolled to finished gage, finished for example by passage through a temper mill to improve its shape and by side trimming, and sold to the customer who anneals it in a magnetic annealing step.

The magnetic annealing is preferably carried out over a period ranging from 20 minutes to 4 hours at a temperature ranging from about 1,250 to about 1,3 F. very preferably in a non-decarburizing atmosphere. These are relatively low temperatures inasmuch as magnetic annealing is usually carried out at l,450 F. Thus in enabling the use of temperatures less than 1,450" F., this process provides a significant advantage to the customer as described in detail later. Annealing for example can be carried out very satisfactorily at l,350 F. for one hour; higher temperatures, for example up to about 1,450 E, and longer annealing times can be used but do not significantly improve the perpercent to about 0.015 percent carbon and from abut I50 p.p.m. to about 350 p.p.m. oxygen. Any number of formance of the product.

The annealed product is suitable for electrical purposes. Typical core losses for product of nominal gage of 0.024 inch range from 4.4 to 4.9 watts per pound and for product of nominal gage of 0.028 inch range from 5.4 to 5.9 watts per pound. Typical permeabilities for product with a nominal gage of 0.024 inch range from 2,400 to 3,200 gausses per oersted and for product with a nominal gage of 0.028 inch range from 1,400 to 2,200 gausses per oersted.

In a somewhat different process, the pickled product is cold rolled to an intermediate gage, then is batch annealed at a temperature ranging from about l,200 to about 1,330" F. for from about 8 to about 30 hours and then is cold worked to obtain from about 0.5 percent to about 2 percent elongation for example utilizing a temper mill. The resulting product is referred to as temper rolled product. This product is not necessarily magnetically annealed by the customer. If it is magnetically annealed, the same ranges of times and temperatures are used as disclosed above for the product of this invention which is not subjected to any elongation after cold rolling. With batch annealing at l,300 F. for 12 hours, cold working to obtain an elongation of 1 percent and magnetic annealing, typical core losses for a product having a nominal gage of 0.018 inch range from 3.7 to 4.3 watts per pound, for a product having a nominal gage of 0.024 inch range from 4.7

r to 5.3 watts per pound and for a product having a nominal gage of 0.028 inch range from 5.7 to 6.3 watts per pound. With batch annealing at l,300 F. for 12 hours, cold working to obtain an elongation of 1 percent and no magnetic annealing, typical core losses for a product having a nominal gage of 0.018 inch range from 4.5 to 5.5 watts per pound, for a product having a nominal gage of 0.024 inch range from 5.5 to 6.5 watts per pound and for a product having a nominal gage of 0.028 inch range from 6.5 to 7.5 watts per pound.

in a very preferred variant, pickled product is cold rolled to an intermediate gage, then is annealed, then is cold worked to obtain an elongation ranging from 6 to about 15 percent, preferably from about 7 to about 10 percent. The resulting product is referred to as stress rolled product. This product exhibits significantly enhanced electrical properties (as measured after magnetic annealing) compared to product produced utilizing no cold working or a lesser amount of cold working subsequent to cold rolling.

The annealing that precedes the elongation can be batch (box) or continuous. The batch annealing is typically carried out at a temperature ranging from l,l50 to l,250 F. for a time period ranging from 5 to 8 hours. In a typical continuous annealing step the cold rolled material is processed for example at 1,000 feet per minute at a temperature ranging from l,lO to l,250 F.; such processing takes less than minutes. The continuous annealing step is preferred over the batch annealing step inasmuch as it provides finished product with a core loss of 0.2 to 0.3 watts per pound less than the finished product obtained after batch annealing.

The stress rolled product can be finished for example by side trimming and possibly varnishing and then is ready for sale.

After magnetic anneal by the customer utilizing the times and temperatures discussed previously for the product of this invention which is not subjected to any elongation after cold rollin g, the product has excellent electrical properties. Typical core losses for a product of nominal gage of 0.018 inch range from 2.7 to 3.3 watts per pound, for a product of nominal gage of 0.024 inch range from 3.7 to 4.3 watts per pound and for a product of nominal gage of 0.028 inch range from 4.7 to 5.3 watts per pound. Typical permeabilities for a product of 0.01 8 inch gage range from 2,300 to 3,100 gausses per oersted, for a product having a nominal gage of 0.024 inch range from 2,400 to 3,400 gausses per oersted, and for a product of nominal gage of 0.028 inch range from 2,100 to 2,900 gausses per oersted. These typical core losses and permeabilities pertain to stress rolled product that was continuously annealed prior to cold working.

The above described processes enable a magnetic annealing step at a temperature lower than the conventional temperature of l,450 F. This enables the customer who typically carries out this magnetic annealing step to speed production and save fuel. In addition, the use of a lower temperature minimizes sticking hazard 4 during annealing, that is minimizes the chances of laminations sticking to one another during the annealing step.

It has been discovered that in the above described processes the inclusion of phosphorus provides advantages. This phosphorus is conveniently added as ferrophosphorus in the ladle. The inclusion of this phosphorus provides a product of improved punchability and machinability. In addition, the inclusion of phosphorus improves the electrical properties. The phosphorus is added to provide a maximum percentage in the finished product of 0.15 percent. It has been discovered that the addition of phosphorus to provide 0.03 to 0.06 percent in the finished product provides a core loss improvement of about 0.2 watts per pound, to provide from 0.06 to 0.09 percent in the finished product provides a core loss improvement of 0.4 watts per pound and to provide 0.09 to 0.15 percent in the finished product provides a core loss improvement of 0.5 watts per pound. The inclusion of this phosphorus is especially desirable at levels ranging from 0.03 to 0.15 percent in the stress rolled product which is batch annealed prior to cold working.

It has also been discovered that the inclusion or manganese is also desirable. This manganese can be added as ferromanganese in the ladle. Levels of about 0.25 percent to about 1 percent are useful with levels of 0.3 to 0.6 percent preferred. The inclusion of this manganese improves the electrical properties slightly, that is it improves core loss on the order of 0.1 watts per pound or less.

The steels manufactured by the above described processes are non-silicon bearing, that is they contain no added silicon. They contain, however, as much as 0.3 percent silicon as a residual material. 1

The following examples illustrate the above described processes. In each of the examples, the finished product contains no added silicon and only 0.01 percent silicon as residual material.

EXAMPLE I Steel from a basic oxygen furnace having phosphorus and manganese added to it in the form of ferromanganese and ferrophosphorus, such addition taking place in the ladle, contains 0.05 percent by weight carbon and 500 p.p.m. by weight oxygen and sufficient manganese and phosphorus to provide 0.45 percent manganese and 0.05 percent phosphorus in the finished product. The steel in molten condition in the ladle is degassed utilizing an R-H degassing process to reduce the carbon content to 0.01 percent and the oxygen content to 200 p.p.m. After degassing, the steel is cast into ingots and slabbed in a blooming mill. The slab is hot rolled with a temperature leaving the finishing train of 1,500" F. and coiled at a temperature of l,325 F. The coiled. material is pickled utilizing a four tank system with the tanks containing aqueous sulfuric acid solution at concentrations ranging from 10 to 20 percent by volume. The pickled material is cold rolled to a nominal gage of 0.024 inches. Then the material is run through a temper mill to improve its shape and side trimmed. The material so produced is laboratory annealed at 1,350" F. for one hour in a nondecarburizing atmosphere.

The annealed material has an average core loss of 4.7 watts per pound and a permeability of 2,800 gausses per oersted. It is suitable for use as an electrical steel and is readily punchable and machinable.

EXAMPLE 11 Example I is duplicated up through the pickling step. The material is then cold rolled to an intermediate gage and then is batch annealed for 12 hours. The annealed material is cold worked in a temper mill to obtain a 1 percent elongation for a final nominal gage of 0.024 inches. After magnetic annealing at l,350 F. for 1 hour in a non-decarburizing atmosphere the material has a core loss of 5.0 watts per pound and a permeability of 2,800 gausses per oersted. With no magnetic annealing, the material has a core loss of 5.8 watts per pound.

EXAMPLE Ill Material is produced the same as Example 1 up through the pickling step. The pickled material is cold rolled to intermediate gage and then is continuously annealed at a temperature ranging from 1,100 to l,250 F. by passage through a continuous annealing furnace at 1,000 feet per minute, the residence time in the furnace being less than 5 minutes. The continuously annealed material is cold worked to obtain an elongation of 8 percent utilizing a two stand mill lubricated with water and cleaning solution with an air knife taking water and cleaning solution off the strip as it issues from the mill. The issuing material is side trimmed and has a finished gage of 0.024 inches. After a laboratory anneal at 1,350 F. for 1 hour in a nondecarburizing atmosphere, it has a core loss of 4.0 watts per pound and a permeability of 3,400 gausses per oersted. 1t is an excellent electrical steel and is readily punchable and machined.

EXAMPLE 1V Material is processed as in Example 111 except instead of a continuous annealing step a batch annealing step is utilized. The batch annealing is at 1,200 F. for 6 hours. The core loss is 4.2 watts per pound and the permeability is 3,400 gausses per oersted.

The percentages and parts mentioned herein except with respect to elongation and except as otherwise stated are by weight. Core losses mentioned herein are as determined at 15 kilogausses, l 10 volts and 60 cycles per second utilizing equipment in accordance with ASTM standard methods A 34 and A 343. Penneabilities are as determined utilizing equipment in accordance with ASTM standard methods A 34 and A 343.

The invention may be embodied in other specific forms without departing from the spirit or the essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all which comes within the meaning and range of equivalency of the claims is intended to be embraced therein.

We claim:

1. Method for producing non-silicon bearing electrical steel characterized after a magnetic anneal by a core loss not exceeding 3.3 watts per pound for a product of nominal gage of 0.018 inch, not exceeding 4.3 watts per pound for a product of nominal gage of 0.024 inch, and not exceeding 5.3 watts per pound for a prod- 6 uct of nominal gage of 0.028 inch, said method being carried out without open coil annealing, said method comprising the steps of a. providing steel in molten condition consisting essentially by weight of iron, from 0.03 to about 0.07 percent carbon, from about 300 p.p.m. to about 800 p.p.m. oxygen, from about 0.03 percent to about 0.15 percent phosphorus as measured subsequent to step (b), and from about 0.25 percent to about 1 percent manganese as measured subsequent to step (b),

b. degassing said steel to reduce the percentage of carbon below 0.03 percent to a level exceeding 0.002 percent;

c. forming the degassed material into slabs;

d. hot rolling with the temperature of the material leaving the finishing train ranging from about 1,450 to about l,550 F.;

e. coiling at a temperature ranging from about 1,25 0

to about l,400 F.;

f. pickling;

g. cold rolling;

h. annealing continuously;

i. cold working to obtain from 6 percent to about 15 percent elongation.

2. Method as recited in claim 1 in which material leaves the hot rolling step at a temperature ranging from about 1,475 to about l,525 F. and is coiled at a temperature ranging from about 1,300 to about l,350 F.

3. Method for producing non-silicon bearing electrical steel characterized after a magnetic anneal by a core loss not exceeding 3.6 watts per pound for a product of nominal gage of 0.018 inch, not exceeding 4.6 watts per pound for a product of nominal gage of 0.024 inch, and not exceeding 5.6 watts per pound for a product of nominal gage of 0.028 inch, said method being carried out without open coil annealing, said method comprising the steps of a. providing steel in molten condition consisting essentially by weight of iron, from 0.03 to about 0.07 percent carbon, from about 300 p.p.m. to about 800 p.p.m. oxygen, from about 0.03 percent to about 0.15 percent phosphorus as measured subsequent to step (b), and from about 0.25 percent to about 1 percent manganese as measured subsequent to step (b);

b. degassing said steel to reduce the percentage of carbon below 0.03 percent to a level exceeding 0.002 percent;

0. forming the degassed material into slabs;

(1. hot rolling with the temperature of the material leaving the finishing train ranging from about 1,450 to about 1,550 F.;

e. coiling at a temperature ranging from about l,250

to about 1,400 F f. pickling;

g. cold rolling;

h. box annealing at a temperature ranging from 1,150 to l,250 F. for a time period ranging from 5 to 8 hours;

i. cold working to obtain from 6 percent to about 15 percent elongation.

4. Method as recited in claim 3 in which material leaves the hot rolling step at a temperature ranging from about 1,475 to about 1,525 F. and is coiled at a temperature ranging from about l,300 to about l,350 F. 

2. Method as recited in claim 1 in which material leaves the hot rolling step at a temperature ranging from about 1,475* to about 1,525* F. and is coiled at a temperature ranging from about 1, 300* to about 1,350* F.
 3. Method for producing non-silicon bearing electrical steel characterized after a magnetic anneal by a core loss not exceeding 3.6 watts per pound for a product of nominal gage of 0.018 inch, not exceeding 4.6 watts per pound for a product of nominal gage of 0.024 inch, and not exceeding 5.6 watts per pound for a product of nominal gage of 0.028 inch, said method being carried out without open coil annealing, said method comprising the steps of a. providing steel in molten condition consisting essentially by weight of iron, from 0.03 to about 0.07 percent carbon, from about 300 p.p.m. to about 800 p.p.m. oxygen, from about 0.03 percent to about 0.15 percent phosphorus as measured subsequent to step (b), and from about 0.25 percent to about 1 percent manganese as measured subsequent to step (b); b. degassing said steel to reduce the percentage of carbon below 0.03 percent to a level exceeding 0.002 percent; c. forming the degassed material into slabs; d. hot rolling with the temperature of the material leaving the finishing train ranging from about 1,450* to about 1,550* F.; e. coiling at a temperature ranging from about 1,250* to about 1,400* F.; f. pickling; g. cold rolling; h. box annealing at a temperature ranging from 1,150* to 1,250* F. for a time period ranging from 5 to 8 hours; i. cold working to obtain from 6 percent to about 15 percent elongation.
 4. Method as recited in claim 3 in which material leaves the hot rolling step at a temperature ranging from about 1,475* to about 1,525* F. and is coiled at a temperature ranging from about 1, 300* to about 1,350* F. 